Laser processing method, method for manufacturing semiconductor device, and inspecting device

ABSTRACT

An inspecting device includes a stage configured to support a wafer in which a plurality of rows of modified regions are formed in a semiconductor substrate, a light source configured to output light, an objective lens configured to pass light propagated through the semiconductor substrate, a light detection part configured to detect light passing through the objective lens, and an inspection part configured to inspect whether or not there is a tip of a fracture in an inspection region between a front surface and the modified region closest to the front surface of the semiconductor substrate. The objective lens positions a virtual focus symmetrical with a focus with respect to the front surface in the inspection region. The light detection part detects light propagating from the back surface side of the semiconductor substrate to the back surface side via the front surface.

TECHNICAL FIELD

The present disclosure relates to a laser processing method, a methodfor manufacturing a semiconductor device, and an inspecting device.

BACKGROUND ART

A laser processing device that, in order to cut a wafer including asemiconductor substrate and a functional element layer formed on thefront surface of the semiconductor substrate, along each of a pluralityof lines, forms a plurality of rows of modified regions in thesemiconductor substrate along each of the plurality of lines byirradiating the wafer with laser light from the back surface side of thesemiconductor substrate is known. The laser processing device disclosedin Patent Literature 1 includes an infrared camera, and thus is capableof observing the modified region formed in the semiconductor substrate,a processing damage formed in the functional element layer, and the likefrom the back surface side of the semiconductor substrate.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No.2017-64746

SUMMARY OF INVENTION Technical Problem

In the laser processing device as described above, the wafer may beirradiated with laser light from the back surface side of thesemiconductor substrate under a condition that a fracture extendingthrough the plurality of rows of modified regions is formed. In such acase, if the fracture extending through the plurality of rows ofmodified regions is not sufficiently extended to the front surface sideof the semiconductor substrate due to, for example, a problem of thelaser processing device, it may not be possible to reliably cut thewafer along each of the plurality of lines in the subsequent steps. Inparticular, in a case where the back surface of the semiconductorsubstrate is ground after the modified regions are formed, if it is notpossible to check whether or not the fracture extending through theplurality of rows of modified regions is sufficiently extended to thefront surface side of the semiconductor substrate, it is not possible toreliably cut the wafer along each of the plurality of lines after thegrinding step, and the grinding step may be useless.

It is difficult to check whether or not the fracture extending throughthe plurality of rows of modified regions is sufficiently extended tothe front surface side of the semiconductor substrate only by observingthe modified regions. Observation of the fracture extending through theplurality of rows of modified regions is also considered, but it isdifficult to observe the fracture simply by using an infrared camerabecause the width of the fracture is usually smaller than the wavelengthof infrared rays.

An object of the present disclosure is to provide a laser processingmethod, a method for manufacturing a semiconductor device, and aninspecting device capable of checking whether or not fracture extendingthrough a plurality of rows of modified regions is sufficiently extendedto a front surface side of a semiconductor substrate.

Solution to Problem

According to an aspect of the present disclosure, a laser processingmethod includes a first step of preparing a wafer including asemiconductor substrate having a front surface and a back surface and afunctional element layer formed on the front surface, and forming aplurality of rows of modified regions in the semiconductor substratealong each of a plurality of lines by irradiating the wafer with laserlight from the back surface side along each of the plurality of lines,and a second step of inspecting whether or not there is a tip of afracture in an inspection region between the front surface and themodified region closest to the front surface among the plurality of rowsof modified regions, the fracture extending to the front surface sidefrom the modified region closest to the front surface. In the firststep, the wafer is irradiated with the laser light from the back surfaceside along each of the plurality of lines under a condition that afracture extending through the plurality of rows of modified regions isformed, and, in the second step, whether or not there is the tip in theinspection region is inspected by aligning a focus from the back surfaceside to a region on an opposite side of the back surface with respect tothe front surface, positioning a virtual focus symmetrical with thefocus with respect to the front surface in the inspection region, anddetecting light propagating in the semiconductor substrate from the backsurface side to the back surface side via the front surface.

In the laser processing method, the focus is aligned from the backsurface side to the region on an opposite side of the back surface ofthe semiconductor substrate with respect to the front surface of thesemiconductor substrate, the virtual focus symmetrical with the focuswith respect to the front surface is positioned in the inspection region(inspection region between the front surface and the modified regionclosest to the front surface of the semiconductor substrate), and thelight propagating in the semiconductor substrate from the back surfaceside to the back surface side via the front surface is detected. Sincethe light is detected in this manner, it is possible to check the tip ina case where there is the tip of the fracture extending to the frontsurface side from the modified region closest to the front surface ofthe semiconductor substrate, in the inspection region. Thus, accordingto the laser processing method, it is possible to check whether or notthe fracture extending through the plurality of rows of modified regionsis sufficiently extend to the front surface side of the semiconductorsubstrate.

In the laser processing method in the aspect of the present disclosure,in the first step, the wafer may be irradiated with the laser light fromthe back surface side along each of the plurality of lines under acondition that the fracture extending through the plurality of rows ofmodified regions reaches the front surface. In a case where there is thetip of the fracture extending to the front surface side from themodified region closest to the front surface of the semiconductorsubstrate, in the inspection region (inspection region between the frontsurface and the modified region closest to the front surface of thesemiconductor substrate), it is assumed that the fracture extendingthrough the plurality of rows of modified regions does not reach thefront surface of the semiconductor substrate. Thus, it is possible tocheck whether or not the fracture extending through the plurality ofrows of modified regions reaches the front surface of the semiconductorsubstrate.

According to the one aspect of the present disclosure, the laserprocessing method may further include a third step of evaluating aprocessing result in the first step, based on an inspection result inthe second step. In the third step, it may be evaluated that thefracture extending through the plurality of rows of modified regionsreaches the front surface, in a case where there is no tip in theinspection region, and may be evaluation that the fracture extendingthrough the plurality of rows of modified regions does not reach thefront surface, in a case where there is the tip in the inspectionregion. According to this, it is possible to determine an embodiment ofthe subsequent steps based on the evaluation result.

In the laser processing method in the one aspect of the presentdisclosure, the plurality of rows of modified regions may be two rows ofmodified regions. According to this, it is possible to efficientlyperform the formation of a plurality of rows of modified regions and theinspection of the fracture extending through the plurality of rows ofmodified regions.

According to another aspect of the present disclosure, a method formanufacturing a semiconductor device includes the first step, the secondstep, and the third step in the above-described laser processing method,and a fourth step, in a case where it is evaluated that the fractureextending through the plurality of rows of modified regions reaches thefront surface in the third step, exposing the fracture extending throughthe plurality of rows of modified regions to the back surface bygrinding the back surface, and cutting the wafer into a plurality ofsemiconductor devices along each of the plurality of lines.

According to the method for manufacturing a semiconductor device, in acase where it is evaluated that the fracture extending through theplurality of rows of modified regions does not reach the front surfaceof the semiconductor substrate, the back surface of the semiconductorsubstrate is not ground. Thus, it is possible to prevent an occurrenceof a situation in which it is not possible to reliably cut a wafer alongeach of a plurality of lines after the grinding step.

According to still another aspect of the present disclosure, aninspecting device includes a stage configured to support a waferincluding a semiconductor substrate having a front surface and a backsurface and a functional element layer formed on the front surface, thewafer in which a plurality of rows of modified regions are formed in thesemiconductor substrate along each of a plurality of lines, a lightsource configured to output light having transparency to thesemiconductor substrate, an objective lens configured to pass the lightoutput from the light source and propagated through the semiconductorsubstrate, a light detection part configured to detect the light passingthrough the objective lens, and an inspection part configured to inspectwhether or not there is a tip of a fracture in an inspection regionbetween the front surface and the modified region closest to the frontsurface among the plurality of rows of modified regions, based on asignal output from the light detection part, the fracture extending fromthe modified region closest to the front surface to the front surfaceside. The objective lens aligns a focus from the back surface side to aregion on an opposite side of the back surface with respect to the frontsurface and positions a virtual focus symmetrical with the focus withrespect to the front surface, in the inspection region. The lightdetection part detects the light propagating in the semiconductorsubstrate from the back surface side to the back surface side via thefront surface.

In the inspecting device, the focus is aligned from the back surfaceside to the region on an opposite side of the back surface of thesemiconductor substrate with respect to the front surface of thesemiconductor substrate, the virtual focus symmetrical with the focuswith respect to the front surface is positioned in the inspection region(inspection region between the front surface and the modified regionclosest to the front surface of the semiconductor substrate), and thelight propagating in the semiconductor substrate from the back surfaceside to the back surface side via the front surface is detected. Sincethe light is detected in this manner, it is possible to check the tip ina case where there is the tip of the fracture extending to the frontsurface side from the modified region closest to the front surface ofthe semiconductor substrate, in the inspection region.

In the inspecting device in the aspect of the present disclosure, thenumerical aperture of the objective lens may be 0.45 or more. Accordingto this, it is possible to more reliably check the tip of the fracturein the inspection region.

In the inspecting device in the one aspect of the present disclosure,the objective lens may have a correction ring. According to this, it ispossible to more reliably check the tip of the fracture in theinspection region.

Advantageous Effects of Invention

According to the present disclosure, it is possible to provide a laserprocessing method, a method for manufacturing a semiconductor device,and an inspecting device capable of checking whether or not fractureextending through a plurality of rows of modified regions issufficiently extended to a front surface side of a semiconductorsubstrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram illustrating a laser processing deviceincluding an inspecting device according to an embodiment.

FIG. 2 is a plan view illustrating a wafer in the embodiment.

FIG. 3 is a cross-sectional view illustrating a portion of the waferillustrated in FIG. 2.

FIG. 4 is a configuration diagram illustrating a laser irradiation unitillustrated in FIG. 1.

FIG. 5 is a configuration diagram illustrating an inspection imagecapturing unit illustrated in FIG. 1.

FIG. 6 is a configuration diagram illustrating an alignment correctionimage capturing unit illustrated in FIG. 1.

FIG. 7 is a cross-sectional view illustrating a wafer for explaining theimage capturing principle by the inspection image capturing unitillustrated in FIG. 5, and is an image at each location by theinspection image capturing unit.

FIG. 8 is a cross-sectional view illustrating the wafer for explainingthe image capturing principle by the inspection image capturing unitillustrated in FIG. 5, and is an image at each location by theinspection image capturing unit.

FIG. 9 is an SEM image of a modified region and a fracture formed in asemiconductor substrate.

FIG. 10 is an SEM image of the modified region and the fracture formedin the semiconductor substrate.

FIG. 11 is an optical path diagram for explaining the image capturingprinciple by the inspection image capturing unit illustrated in FIG. 5,and is a schematic diagram illustrating an image at a focus by theinspection image capturing unit.

FIG. 12 is an optical path diagram for explaining the image capturingprinciple by the inspection image capturing unit illustrated in FIG. 5,and is a schematic diagram illustrating an image at the focus by theinspection image capturing unit.

FIG. 13 is a cross-sectional view illustrating a wafer for explainingthe inspection principle by the inspection image capturing unitillustrated in FIG. 5, and is an image of a cut surface of the wafer andan image at each location by the inspection image capturing unit.

FIG. 14 is a cross-sectional view illustrating a wafer for explainingthe inspection principle by the inspection image capturing unitillustrated in FIG. 5, and is an image of a cut surface of the wafer andan image at each location by the inspection image capturing unit.

FIG. 15 is a flowchart illustrating a method for manufacturing asemiconductor device in the embodiment.

FIG. 16 is a cross-sectional view illustrating a portion of a wafer ingrinding and cutting steps in the method for manufacturing asemiconductor device illustrated in FIG. 15.

FIG. 17 is a cross-sectional view illustrating a portion of a wafer ingrinding and cutting steps in the method for manufacturing asemiconductor device illustrated in FIG. 15.

FIG. 18 is a configuration diagram illustrating a laser processingsystem including an inspecting device according to a modificationexample.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the drawings. The same or corresponding partsin the respective drawings are denoted with the same reference signs,and repetitive descriptions will be omitted.

[Configuration of Laser Processing Device]

As illustrated in FIG. 1, a laser processing device 1 includes a stage2, a laser irradiation unit 3, a plurality of image capturing units 4, 5and 6, a drive unit 7, and a control unit 8. The laser processing device1 is a device that forms a modified region 12 on an object 11 byirradiating the object 11 with laser light L.

The stage 2 supports the object 11 by, for example, adsorbing a filmattached to the object 11. The stage 2 can move along an X-direction anda Y-direction, respectively, and can rotate around an axis parallel to aZ-direction as a center line. The X-direction and the Y-direction arereferred to as a first horizontal direction and a second horizontaldirection that are perpendicular to each other, and the Z-direction isthe vertical direction.

The laser irradiation unit 3 collects the laser light L havingtransparency to the object 11 and the object 11 with the laser light. Ifthe laser light L is focused in the object 11 supported by the stage 2,the laser light L is particularly absorbed at a portion corresponding toa focusing point C of the laser light L, and thus the modified region 12is formed in the object 11.

The modified region 12 is a region in which the density, the refractiveindex, the mechanical strength, and other physical properties aredifferent from those of the surrounding non-modified region. Examples ofthe modified region 12 include a melting treatment region, a crackregion, a dielectric breakdown region, and a refractive index changeregion. The modified region 12 has a characteristic that fractureseasily extend from the modified region 12 to the incident side of thelaser light L and the opposite side. Such characteristics of themodified region 12 are used for cutting the object 11.

As an example, if the stage 2 is moved along the X-direction and thefocusing point C is moved relative to the object 11 along theX-direction, a plurality of modified spots 12 s are formed to bearranged in one row along the X-direction. One modified spot 12 s isformed by irradiation with the laser light L of one pulse. The modifiedregion 12 in one row is a set of a plurality of modified spots 12 sarranged in one row. Adjacent modified spots 12 s may be connected toeach other or separated from each other, depending on the relativemovement speed of the focusing point C with respect to the object 11 andthe repetition frequency of the laser light L.

The image capturing unit 4 captures images of the modified region 12formed on the object 11 and the tip of the fracture extending from themodified region 12. In the present embodiment, the control unit 8functions as an inspection part, and the stage 2, the image capturingunit 4, and the control unit 8 function as an inspecting device 10(details will be described later).

Under the control of the control unit 8, the image capturing units 5 and6 capture an image of the object 11 supported by the stage 2 with lighttransmitted through the object 11. The images obtained by the imagecapturing units 5 and 6 performing image capturing are, for example,used for alignment of the irradiation position of the laser light L.

The drive unit 7 supports the laser irradiation unit 3 and a pluralityof image capturing units 4, 5, and 6. The drive unit 7 moves the laserirradiation unit 3 and the plurality of image capturing units 4, 5, 6along the Z-direction.

The control unit 8 controls the operations of the stage 2, the laserirradiation unit 3, the plurality of image capturing units 4, 5, 6, andthe drive unit 7. The control unit 8 is configured as a computer deviceincluding a processor, a memory, a storage, a communication device, andthe like. In the control unit 8, the processor executes software(program) read into the memory or the like, and controls reading andwriting of data in the memory and the storage, and communication by acommunication device. Thus, the control unit 8 realizes, for example, afunction as an inspection part (details will be described later).

[Configuration of Object]

The object 11 in the present embodiment is a wafer 20 as illustrated inFIGS. 2 and 3. The wafer 20 includes a semiconductor substrate 21 and afunctional element layer 22. The semiconductor substrate 21 has a frontsurface 21 a and a back surface 21 b. The semiconductor substrate 21 is,for example, a silicon substrate. The functional element layer 22 isformed on the front surface 21 a of the semiconductor substrate 21. Thefunctional element layer 22 includes a plurality of functional elements22 a arranged two-dimensionally along the front surface 21 a. Thefunctional element 22 a is, for example, a light receiving element suchas a photodiode, a light emitting element such as a laser diode, acircuit element such as a memory, or the like. The functional element 22a may be configured three-dimensionally by stacking a plurality oflayers. Although the semiconductor substrate 21 is provided with a notch21 c indicating the crystal orientation, an orientation flat may beprovided instead of the notch 21 c.

The wafer 20 is cut into functional elements 22 a along each of theplurality of lines 15. The plurality of lines 15 pass between aplurality of functional elements 22 a in a case of being viewed from thethickness direction of the wafer 20. More specifically, the line 15passes through the center (center in the width direction) of a streetregion 23 in a case of being viewed from the thickness direction of thewafer 20. The street region 23 extends to pass between adjacentfunctional elements 22 a in the functional element layer 22. In thepresent embodiment, the plurality of functional elements 22 a arearranged in a matrix along the front surface 21 a, and the plurality oflines 15 are set in a grid. Although the line 15 is a virtual line, theline may be a line actually drawn.

[Configuration of Laser Irradiation Unit]

As illustrated in FIG. 4, the laser irradiation unit 3 includes a lightsource 31, a spatial light modulator 32, and a condenser lens 33. Thelight source 31 outputs the laser light L by, for example, a pulseoscillation method. The spatial light modulator 32 modulates the laserlight L output from the light source 31. The spatial light modulator 32is, for example, a spatial light modulator (SLM) of a reflective liquidcrystal (LCOS: Liquid Crystal on Silicon). The condenser lens 33collects the laser light L modulated by the spatial light modulator 32.

In the present embodiment, the laser irradiation unit 3 irradiates thewafer 20 with the laser light L from the back surface 21 b side of thesemiconductor substrate 21 along each of the plurality of lines 15, soas to form two rows of modified regions 12 a and 12 b in thesemiconductor substrate 21 along each of the plurality of lines 15. Themodified region (first modified region) 12 a is the modified regionclosest to the front surface 21 a of the two rows of modified regions 12a and 12 b. The modified region (second modified region) 12 b is themodified region closest to the modified region 12 a among two rows ofthe modified regions 12 a and 12 b, and is the modified region closestto the back surface 21 b.

The two rows of modified region 12 a and 12 b are adjacent to each otherin the thickness direction (Z-direction) of the wafer 20. The two rowsof modified regions 12 a and 12 b are formed by moving two focusingpoints C1 and C2 relative to the semiconductor substrate 21 along theline 15. The laser light L is modulated by the spatial light modulator32 so that, for example, the focusing point C2 is located on the rearside in a traveling direction and on the incident side of the laserlight L with respect to the focusing point C1.

The laser irradiation unit 3 irradiates the wafer 20 with the laserlight L from the back surface 21 b side of the semiconductor substrate21 along each of the plurality of lines 15 under a condition that afracture 14 extending through the two rows of modified regions 12 a and12 b reaches the front surface 21 a of the semiconductor substrate 21.As an example, for the semiconductor substrate 21 which is a singlecrystal silicon substrate having a thickness of 775 μm, the two focusingpoints C1 and C2 are aligned at positions of 54 μm and 128 μm from thefront surface 21 a. Then, the wafer 20 is irradiated with the laserlight L from the back surface 21 b side of the semiconductor substrate21 along each of the plurality of lines 15. At this time, the wavelengthof the laser light L is 1099 nm, the pulse width is 700 nsec, and therepetition frequency is 120 kHz. In addition, the output of the laserlight L at the focusing point C1 is 2.7 W, the output of the laser lightL at the focusing point C2 is 2.7 W, and the relative movement speeds ofthe two focusing points C1 and C2 with respect to the semiconductorsubstrate 21 are 800 mm/sec.

The formation of such two rows of modified regions 12 a, 12 b andfracture 14 is performed in the following cases. That is, in a casewhere, in the subsequent steps, the back surface 21 b of thesemiconductor substrate 21 is ground to thin the semiconductor substrate21 and expose the fracture 14 to the back surface 21 b, and the wafer 20is cut into a plurality of semiconductor devices along each of theplurality of lines 15, such formation is performed.

[Configuration of Inspection Image Capturing Unit]

As illustrated in FIG. 5, the image capturing unit 4 includes a lightsource 41, a mirror 42, an objective lens 43, and a light detection part44. The light source 41 outputs light I1 having transparency to thesemiconductor substrate 21. The light source 41 is configured by, forexample, a halogen lamp and a filter, and outputs light I1 in the nearinfrared region. The light I1 output from the light source 41 isreflected by the mirror 42, passes through the objective lens 43, andthen is applied to the wafer 20 from the back surface 21 b side of thesemiconductor substrate 21. At this time, the stage 2 supports the wafer20 in which the two rows of modified regions 12 a and 12 b are formed asdescribed above.

The objective lens 43 passes the light I1 reflected by the front surface21 a of the semiconductor substrate 21 through the objective lens. Thatis, the objective lens 43 passes the light I1 propagating in thesemiconductor substrate 21 through the objective lens. The numericalaperture (NA) of the objective lens 43 is 0.45 or more. The objectivelens 43 includes a correction ring 43 a. The correction ring 43 acorrects the aberration generated in the light I1 in the semiconductorsubstrate 21 by adjusting the distance between a plurality of lensesconstituting the objective lens 43, for example. The light detectionpart 44 detects the light I1 that has passed through the objective lens43 and the mirror 42. The light detection part 44 is configured by, forexample, an InGaAs camera, and detects the light I1 in the near infraredregion.

The image capturing unit 4 is capable of capturing images of each of thetwo rows of modified regions 12 a and 12 b and the tip of each of aplurality of fractures 14 a to 14 d (details will be described later).The fracture 14 a is a fracture extending from the modified region 12 ato the front surface 21 a side. The fracture 14 b is a fractureextending from the modified region 12 a to the back surface 21 b side.The fracture 14 c is a fracture extending from the modified region 12 bto the front surface 21 a side. The fracture 14 d is a fractureextending from the modified region 12 b to the back surface 21 b side.The control unit 8 causes the laser irradiation unit 3 to performirradiation with the laser light L under the condition that the fracture14 extending through the two rows of modified regions 12 a and 12 breaches the front surface 21 a of the semiconductor substrate 21 (seeFIG. 4). If the fracture 14 does not reach the front surface 21 a due toany problem or the like, the plurality of such fractures 14 a to 14 dare formed.

[Configuration of Alignment Correction Image Capturing Unit]

As illustrated in FIG. 6, the image capturing unit 5 includes a lightsource 51, a mirror 52, a lens 53, and a light detection part 54. Thelight source 51 outputs light 12 having transparency to thesemiconductor substrate 21. The light source 51 is configured by, forexample, a halogen lamp and a filter, and outputs light 12 in the nearinfrared region. The light source 51 may be shared with the light source41 of the image capturing unit 4. The light 12 output from the lightsource 51 is reflected by the mirror 52, passes through the lens 53, andthen is applied to the wafer 20 from the back surface 21 b side of thesemiconductor substrate 21.

The lens 53 passes the light 12 reflected by the front surface 21 a ofthe semiconductor substrate 21 through the lens. That is, the lens 53passes the light 12 propagating in the semiconductor substrate 21through the lens. The numerical aperture of the lens 53 is 0.3 or less.That is, the numerical aperture of the objective lens 43 in the imagecapturing unit 4 is more than the numerical aperture of the lens 53. Thelight detection part 54 detects the light 12 that has passed through thelens 53 and the mirror 52. The light detection part 55 is configured by,for example, an InGaAs camera, and detects the light 12 in the nearinfrared region.

Under the control of the control unit 8, the image capturing unit 5captures an image of the functional element layer 22 by irradiating thewafer 20 with the light 12 from the back surface 21 b side and detectingthe light 12 returning from the front surface 21 a (functional elementlayer 22). Further, similarly, under the control of the control unit 8,the image capturing unit 5 acquires an image of a region including themodified regions 12 a and 12 b by irradiating the wafer 20 with thelight 12 from the back surface 21 b side and detecting the light 12returning from positions at which the modified regions 12 a and 12 b areformed in the semiconductor substrate 21. The images are used foralignment of the irradiation position of the laser light L. The imagecapturing unit 6 has the similar configuration to the image capturingunit 5 except that the lens 53 has a lower magnification (for example, 6times in the image capturing unit 5 and 1.5 times in the image capturingunit 6), and is used for alignment, similar to the image capturing unit5.

[Image Capturing Principle by Inspection Image Capturing Unit]

Using the image capturing unit 4 illustrated in FIG. 5, a focus F (focusof the objective lens 43) is moved from the back surface 21 b sidetoward the front surface 21 a side for the semiconductor substrate 21 inwhich the fracture 14 extending through the two rows of modified regions12 a and 12 b reaches the front surface 21 a, as illustrated in FIG. 7.In this case, if the focus F is aligned from the back surface 21 b sideto a tip 14 e of the fracture 14 extending from the modified region 12 bto the back surface 21 b side, it is possible to check the tip 14 e(image on the right side in FIG. 7). However, even though the focus F isaligned to the fracture 14 itself and the tip 14 e of the fracture 14reaching the front surface 21 a from the back surface 21 b side, it isnot possible to check the fracture and the tip of the fracture (image onthe left side in FIG. 7). If the focus F is aligned to the front surface21 a of the semiconductor substrate 21 from the back surface 21 b side,it is possible to check the functional element layer 22.

Further, using the image capturing unit 4 illustrated in FIG. 5, thefocus F is moved from the back surface 21 b side toward the frontsurface 21 a side for the semiconductor substrate 21 in which thefracture 14 extending through the two rows of modified regions 12 a and12 b does not reach the front surface 21 a, as illustrated in FIG. 8. Inthis case, even though the focus F is aligned from the back surface 21 bside to the tip 14 e of the fracture 14 extending from the modifiedregion 12 a to the front surface 21 a side, it is not possible to checkthe tip 14 e (image on the left side in FIG. 8). However, if the focus Fis aligned from the back surface 21 b side to a region on an oppositeside of the back surface 21 b with respect to the front surface 21 a(that is, region on the functional element layer 22 side with respect tothe front surface 21 a), and a virtual focus Fv symmetrical with thefocus F with respect to the front surface 21 a is located at the tip 14e, it is possible to check the tip 14 e (image on the right side in FIG.8). The virtual focus Fv is a point symmetrical with the focus F withrespect to the front surface 21 a in consideration of the refractiveindex of the semiconductor substrate 21.

It is assumed that the reason why it is not possible to check thefracture 14 itself as described above is that the width of the fracture14 is smaller than the wavelength of the light I1 as the illuminationlight. FIGS. 9 and 10 are scanning electron microscope (SEM) images of amodified region 12 and the fracture 14 formed in the semiconductorsubstrate 21 being a silicon substrate. (b) of FIG. 9 is an enlargedimage of a region A1 illustrated in (a) of FIG. 9. (a) of FIG. 10 is anenlarged image of a region A2 illustrated in (b) of FIG. 9. (b) of FIG.10 is an enlarged image of a region A3 illustrated in (a) of FIG. 10. Asdescribed above, the width of the fracture 14 is about 120 nm and issmaller than the wavelength (for example, 1.1 to 1.2 μm) of the light I1in the near infrared region.

The image capturing principle assumed based on the above description isas follows. As illustrated in (a) of FIG. 11, if the focus F is locatedin the air, the light I1 does not return, and thus a blackish image isobtained (image on the right side in (a) of FIG. 11). As illustrated in(b) of FIG. 11, if the focus F is located in the semiconductor substrate21, the light I1 reflected by the front surface 21 a is returned, sothat a whitish image is obtained (image on the right side in (b) of FIG.11). As illustrated in (c) of FIG. 11, if the focus F is aligned on themodified region 12 from the back surface 21 b side, a portion of thelight I1 reflected and returned by the front surface 21 a is absorbed,scattered, and the like by the modified region 12. Thus, an image inwhich the modified region 12 appears blackish in a whitish background isobtained (image on the right side in (c) of FIG. 11).

As illustrated in (a) and (b) of FIG. 12, if the focus F is aligned tothe tip 14 e of the fracture 14 from the back surface 21 b side, forexample, scattering, reflection, interference, absorption, and the likeoccurs in a portion of the light 11 reflected and returned by the frontsurface 21 a by the optical specificity (stress concentration, strain,discontinuity of atomic density, and the like), confinement of light,and the like occurring near the tip 14 e. Thus, an image in which thetip 14 e appears blackish in a whitish background is obtained (images onthe right side in (a) and (b) of FIG. 12). As illustrated in (c) of FIG.12, if the focus F is aligned from the back surface 21 b side to aportion of the fracture 14 other than the vicinity of the tip 14 e ofthe fracture 14, at least a portion of the light I1 reflected by thefront surface 21 a is returned. Thus, a whitish image is obtained (imageon the right side in (c) of FIG. 12).

[Inspection Principle by Inspection Image Capturing Unit]

In a case where, as a result obtained in a manner that the control unit8 causes the laser irradiation unit 3 to perform irradiation with thelaser light L under the condition that the fracture 14 extending throughthe two rows of the modified regions 12 a and 12 b reaches the frontsurface 21 a of the semiconductor substrate 21, the fracture 14extending through the two rows of the modified regions 12 a and 12 breaches the front surface 21 a as planned, the state of the tip 14 e ofthe fracture 14 is as follows. That is, as illustrated in FIG. 13, thetip 14 e of the fracture 14 does not appear in a region between themodified region 12 a and the front surface 21 a and a region between themodified region 12 a and the modified region 12 b. The position (simplyreferred to as a “tip position” below) of the tip 14 e of the fracture14 extending from the modified region 12 b to the back surface 21 b sideis located on the back surface 21 b side with respect to a referenceposition P between the modified region 12 b and the back surface 21 b.

On the other hand, in a case where, as a result obtained in a mannerthat the control unit 8 causes the laser irradiation unit 3 to performirradiation with the laser light L under the condition that the fracture14 extending through the two rows of the modified regions 12 a and 12 breaches the front surface 21 a of the semiconductor substrate 21, thefracture 14 extending through the two rows of the modified regions 12 aand 12 b does not reach the front surface 21 a due to any problem,differing from the plan, the state of the tip 14 e of the fracture 14 isas follows. That is, as illustrated in FIG. 14, the tip 14 e of thefracture 14 a extending from the modified region 12 a to the frontsurface 21 a side appears in the region between the modified region 12 aand the front surface 21 a. The tip 14 e of the fracture 14 b extendingfrom the modified region 12 a to the back surface 21 b and the tip 14 eof the fracture 14 c extending from the modified region 12 b to thefront surface 21 a appear in the region between the modified region 12 aand the modified region 12 b. The tip position of the fracture 14extending from the modified region 12 b to the back surface 21 b side islocated on the front surface 21 a with respect to the reference positionP between the modified region 12 b and the back surface 21 b.

With the above description, if the control unit 8 performs at least oneof the following first inspection, second inspection, third inspection,and fourth inspection, it is possible to evaluate whether or not thefracture 14 extending through the two rows of the modified regions 12 aand 12 b reaches the front surface 21 a of the semiconductor substrate21. The first inspection is an inspection of whether or not, when theregion between the modified region 12 a and the front surface 21 a isset as an inspection region R1, there is the tip 14 e of the fracture 14a extending from the modified region 12 a to the front surface 21 aside, in the inspection region R1. The second inspection is aninspection of whether or not, when the region between the modifiedregion 12 a and the modified region 12 b is set as an inspection regionR2, there is the tip 14 e of the fracture 14 b extending from themodified region 12 a to the back surface 21 b side, in the inspectionregion R2. The third inspection is an inspection of whether or not thereis the tip 14 e of the fracture 14 c extending from the modified region12 b to the front surface 21 a side, in the inspection region R2. Thefourth inspection is an inspection of whether or not, when a region thatextends from the reference position P to the back surface 21 b side anddoes not reach the back surface 21 b is set as an inspection region R3,the tip position of the fracture 14 extending from the modified region12 b to the back surface 21 b side is located in the inspection regionR3.

Each of the inspection region R1, the inspection region R2, and theinspection region R3 can be set based on positions at which the twofocusing points C1 and C2 are aligned with respect to the semiconductorsubstrate 21, before the two rows of modified regions 12 a and 12 b areformed. In a case where the fracture 14 extending through the two rowsof the modified regions 12 a and 12 b reaches the front surface 21 a ofthe semiconductor substrate 21, the tip position of the fracture 14extending from the modified region 12 b to the back surface 21 b side isstable. Thus, the reference position P and the inspection region R3 canbe set based on the result of test processing. As illustrated in FIGS.13 and 14, the image capturing unit 4 is capable of capturing an imageof each of the two modified regions 12 a and 12 b. Thus, after the tworows of modified regions 12 a and 12 b are formed, each of theinspection region R1, the inspection region R2, and the inspectionregion R3 may be set based on the respective positions of the twomodified regions 12 a and 12 b.

[Laser Processing Method and Method for Manufacturing SemiconductorDevice]

The method for manufacturing a semiconductor device in the presentembodiment will be described with reference to FIG. 15. The method formanufacturing a semiconductor device in the present embodiment includesthe laser processing method performed in the laser processing device 1.

Firstly, a wafer 20 is prepared and placed on the stage 2 of the laserprocessing device 1. Then, the laser processing device 1 irradiates thewafer 20 with laser light L from the back surface 21 b side of asemiconductor substrate 21 along each of a plurality of lines 15, so asto form two rows of modified regions 12 a and 12 b in the semiconductorsubstrate 21 along each of the plurality of lines 15 (S01, first step).In this step, the laser processing device 1 irradiates the wafer 20 withthe laser light L from the back surface 21 b side of the semiconductorsubstrate 21 along each of the plurality of lines 15 under a conditionthat fracture 14 extending through the two rows of modified regions 12 aand 12 b reaches the front surface 21 a of the semiconductor substrate21.

The laser processing device 1 inspects whether or not there is a tip 14e of a fracture 14 a extending from the modified region 12 a to thefront surface 21 a side, in an inspection region R1 between the modifiedregion 12 a and the front surface 21 a (S02, second step). In this step,the laser processing device 1 aligns the focus F from the back surface21 b side to a region on an opposite side of the back surface 21 b withrespect to the front surface 21 a, locates a virtual focus Fvsymmetrical with the focus F with respect to the front surface 21 a inthe inspection region R1, and detects light I1 propagating in thesemiconductor substrate 21 from the back surface 21 b side to the backsurface 21 b side via the front surface 21 a. In this manner, the laserprocessing device inspects whether or not there is the tip 14 e of thefracture 14 a in the inspection region R1. As described above, in thepresent embodiment, the laser processing device 1 performs the firstinspection.

More specifically, the objective lens 43 of the image capturing unit 4aligns the focus F from the back surface 21 b side to a region on anopposite side of the back surface 21 b with respect to the front surface21 a, and locates a virtual focus Fv symmetrical with the focus F withrespect to the front surface 21 a in the inspection region R1. Then, thelight detection part 44 of the image capturing unit 4 detects light I1propagating in the semiconductor substrate 21 from the back surface 21 bside to the back surface 21 b side via the front surface 21 a. At thistime, the drive unit 7 moves the image capturing unit 4 along theZ-direction, and the virtual focus Fv is relatively moved in theinspection region R1 along the Z-direction. Thus, the light detectionpart 44 acquires image data at each location in the Z-direction. Thecontrol unit 8 inspects whether or not there is the tip 14 e of thefracture 14 a in the inspection region R1, based on a signal output fromthe light detection part 44 (that is, image data at each location in theZ-direction). As described above, in the present embodiment, the controlunit 8 functions as the inspection part, and the stage 2, the imagecapturing unit 4, and the control unit 8 function as the inspectingdevice 10.

Then, the control unit 8 evaluates the processing result in Step S01based on the inspection result in Step S02 (S03, third step). In thisstep, in a case where there is no tip 14 e of the fracture 14 a in theinspection region R1, the control unit 8 evaluates that the fracture 14extending through the two rows of the modified regions 12 a and 12 breaches the front surface 21 a of the semiconductor substrate 21. On theother hand, in a case where there is the tip 14 e of the fracture 14 ain the inspection region R1, the control unit 8 evaluates that thefracture 14 extending through the two rows of the modified regions 12 aand 12 b does not reach the front surface 21 a of the semiconductorsubstrate 21.

In a case where it is evaluated that the fracture 14 extending throughthe two rows of the modified regions 12 a and 12 b reaches the frontsurface 21 a of the semiconductor substrate 21, the control unit 8performs an acceptance process (S04). In this step, the control unit 8performs, as the acceptance process, for example, display of theacceptance with a display of the laser processing device 1, display ofimage data with the display, recording of the acceptance with a storageunit of the laser processing device 1 (storing as a log), and storing ofimage data with the storage unit. As described above, the display in thelaser processing device 1 functions as a notification unit for notifyingan operator of the acceptance.

On the other hand, in a case where it is evaluated that the fracture 14extending through the two rows of the modified regions 12 a and 12 bdoes not reach the front surface 21 a of the semiconductor substrate 21,the control unit 8 performs a rejection process (S05). In this step, thecontrol unit 8 performs, as the rejection process, for example, lightingof the rejection with a lamp of the laser processing device 1, displayof the rejection with the display of the laser processing device 1, andrecording of the rejection with the storage unit of the laser processingdevice 1 (storing as a log). As described above, at least one of thelamp and the display in the laser processing device 1 functions as thenotification unit for notifying the operator of the rejection.

The above Steps S01 to S05 corresponds to the laser processing methodperformed in the laser processing device 1. A timing of performing thefirst inspection is not limited to a timing after the two rows ofmodified regions 12 a and 12 b are formed in the semiconductor substrate21 along each of all lines 15. The timing for the first inspection maybe a timing after the modified regions 12 a and 12 b are formed along aplurality of lines 15 extending in one direction or a timing which is atiming before the modified regions 12 a and 12 b are further formedalong a plurality of lines 15 extending in one direction and at whichalignment of an irradiation position of the line 15 extending in onedirection with laser light L is performed. Alternatively, the timing ofperforming the first inspection may be a timing at which switching isperformed from formation of the modified regions 12 a and 12 b alongeach of a plurality of lines 15 extending in one direction to formationof the modified regions 12 a and 12 b along each of a plurality of lines15 extending in different directions. A location at which the firstinspection is performed may be at least one of a plurality of lines 15set in a grid. However, in a case where switching is performed from theformation of modified regions 12 a and 12 b along each of the pluralityof lines 15 extending in one direction to the formation of modifiedregions 12 a and 12 b along each of the plurality of lines 15 extendingin different directions, the location at which the first inspection isperformed is preferably a location other than an intersection of thelines 15 extending in different directions (intersection of the line 15extending in the different direction with each of the plurality of lines15 extending in one direction). This is because the state of thefracture 14 tends to be unstable at the intersection of the line 15extending in the different direction.

In a case where the acceptance process in Step S04 is performed (thatis, in a case where it is evaluated in Step 03 that the fracture 14extending through the two rows of the modified regions 12 a and 12 breaches the front surface 21 a of the semiconductor substrate 21), agrinding device grinds the back surface 21 b of the semiconductorsubstrate 21 to expose the fracture 14 extending through the two rows ofthe modified regions 12 a and 12 b to the back surface 21 b and to cutthe wafer 20 into a plurality of semiconductor devices along each of theplurality of lines 15 (S06, fourth step).

The above Steps S01 to S06 corresponds to the method for manufacturing asemiconductor device, which includes the laser processing methodperformed in the laser processing device 1. In a case where therejection process in Step S05 is performed (that is, in a case where itis evaluated in Step 03 that the fracture 14 extending through the tworows of the modified regions 12 a and 12 b does not reach the frontsurface 21 a of the semiconductor substrate 21), examination andadjustment of the laser processing device 1, re-laser processing(recovery processing) on the wafer 20, and the like are performed.

Here, grinding and cutting of the wafer 20 in Step S06 will be describedmore specifically. As illustrated in FIG. 16, a grinding device 200grinds (polishes) the back surface 21 b of the semiconductor substrate21 to thin the semiconductor substrate 21 and expose the fracture 14 tothe back surface 21 b, and the wafer 20 is cut into a plurality ofsemiconductor devices 20 a along each of the plurality of lines 15. Inthis step, the grinding device 200 grinds the back surface 21 b of thesemiconductor substrate 21 to the reference position P for the fourthinspection.

As described above, in a case where the fracture 14 extending throughthe two rows of the modified regions 12 a and 12 b reaches the frontsurface 21 a of the semiconductor substrate 21, the tip position of thefracture 14 extending from the modified region 12 b to the back surface21 b side is located on the back surface 21 b side with respect to thereference position P. Therefore, it is possible to expose the fracture14 extending through the two rows of modified regions 12 a and 12 b tothe back surface 21 b by grinding the back surface 21 b of thesemiconductor substrate 21 to the reference position P. In other words,using a position at which an end of grinding is planned, as thereference position P, the wafer 20 is irradiated with laser light L fromthe back surface 21 b side of the semiconductor substrate 21 along eachof the plurality of lines 15 under the condition that the fracture 14extending through the two rows of modified regions 12 a and 12 b reachesthe front surface 21 a of the semiconductor substrate 21 and thereference position P.

As illustrated in FIG. 17, an expanding device 300 expands an expandingtape 201 attached to the back surface 21 b of the semiconductorsubstrate 21 to separate the plurality of semiconductor devices 20 afrom each other. The expanding tape 201 is, for example, a die attachfilm (DAF) configured by a base material 201 a and an adhesive layer 201b. In this case, the adhesive layer 201 b disposed between the backsurface 21 b of the semiconductor substrate 21 and the base material 201a is cut into the semiconductor devices 20 a by the expansion of theexpanding tape 201. The cut adhesive layer 201 b is picked up togetherwith the semiconductor device 20 a.

Actions and Effects

In the laser processing method described above, the focus F is alignedfrom the back surface 21 b side to the region on the opposite side ofthe back surface 21 b of the semiconductor substrate 21 with respect tothe front surface 21 a of the semiconductor substrate 21, the virtualfocus FIT symmetrical with the focus F with respect to the front surface21 a is located in the inspection region R1, and the light I1propagating in the semiconductor substrate 21 from the back surface 21 bside to the back surface 21 b side via the front surface 21 a isdetected. By detecting the light I1 in this manner, it is possible tocheck the tip 14 e of the fracture 14 a in a case where there is the tip14 e of the fracture 14 a extending from the modified region 12 a to thefront surface 21 a side, in the inspection region R1. It is assumedthat, in a case where there is the tip 14 e of the fracture 14 a in theinspection region R1, the fracture 14 extending through the two rows ofthe modified regions 12 a and 12 b does not reach the front surface 21 aof the semiconductor substrate 21. Thus, according to the laserprocessing method described above, it is possible to check whether ornot the fracture 14 extending through the two rows of modified regions12 a and 12 b reaches the front surface 21 a of the semiconductorsubstrate 21.

Further, in the laser processing method described above, in a case wherethere is no tip 14 e of the fracture 14 a in the inspection region R1,it is evaluated that the fracture 14 extending through the two rows ofmodified regions 12 a and 12 b reaches the front surface 21 a of thesemiconductor substrate 21. In a case where there is the tip 14 e of thefracture 14 a in the inspection region R1, it is evaluated that thefracture 14 extending through the two rows of modified regions 12 a and12 b does not reach the front surface 21 a of the semiconductorsubstrate 21. Accordingly, it is possible to determine an embodiment ofthe subsequent steps based on the evaluation result.

Further, in the laser processing method described above, the two rows ofmodified regions 12 a and 12 b are formed as the plurality of rows ofmodified regions 12. Thus, it is possible to efficiently perform theformation of a plurality of rows of modified regions 12 and theinspection of the fracture 14 extending through the plurality of rows ofmodified regions 12.

Further, according to the above-described method for manufacturing asemiconductor device, in a case where it is evaluated that the fracture14 extending through the two rows of modified regions 12 a and 12 b doesnot reach the front surface 21 a of the semiconductor substrate 21, theback surface 21 b of the semiconductor substrate 21 is not ground. Thus,it is possible to prevent an occurrence of a situation in which it isnot possible to reliably cut a wafer 20 along each of a plurality oflines 15 after the grinding step.

In addition, the inspecting device 10 aligns the focus F from the backsurface 21 b side to the region on the opposite side of the back surface21 b of the semiconductor substrate 21 with respect to the front surface21 a of the semiconductor substrate 21, locates the virtual focus Fvsymmetrical with the focus F with respect to the front surface 21 a inthe inspection region R1, and detects the light I1 propagating in thesemiconductor substrate 21 from the back surface 21 b side to the backsurface 21 b side via the front surface 21 a. By detecting the light I1in this manner, it is possible to check the tip 14 e of the fracture 14a in a case where there is the tip 14 e of the fracture 14 a extendingfrom the modified region 12 a to the front surface 21 a side, in theinspection region R1.

Further, in the inspecting device 10, the numerical aperture of theobjective lens 43 is 0.45 or more. Thus, it is possible to more reliablycheck the tip 14 e of the fracture 14 a in the inspection region R1.

Further, in the inspecting device 10, the objective lens 43 includes thecorrection ring 43 a. Thus, it is possible to more reliably check thetip 14 e of the fracture 14 a in the inspection region R1.

MODIFICATION EXAMPLES

The present disclosure is not limited to the above embodiment. Forexample, in the inspection step of Step S02 illustrated in FIG. 15, thecontrol unit 8 may perform at least one inspection of the secondinspection, the third inspection, and the fourth inspection in additionto the first inspection described above.

In the above-described embodiment, the laser processing device 1 formstwo rows of modified regions 12 a and 12 b in the semiconductorsubstrate 21 along each of the plurality of lines 15, but the laserprocessing device 1 may form three or more rows of modified regions 12in the semiconductor substrate 21 along each of the plurality of lines15. The number of rows, positions, and the like of modified regions 12formed for one line 15 can be appropriately set in consideration of thethickness of the semiconductor substrate 21 in the wafer 20, thethickness of the semiconductor substrate 21 in a semiconductor device 20a, and the like. A plurality of rows of modified regions 12 may beformed by performing the relative movement of the focusing point C ofthe laser light L a plurality of number of times for one line 15.

Further, in the grinding and cutting step of Step S06 illustrated inFIG. 15, the grinding device 200 may grind the back surface 21 b of thesemiconductor substrate 21 beyond the reference position P. The positionat which an end of grinding is planned can be appropriately setdepending on whether or not the modified region 12 is left on the sidesurface (cut surface) of the semiconductor device 20 a. In a case wherethe semiconductor device 20 a is, for example, a dynamic random accessmemory (DRAM), the modified region 12 may remain on the side surface ofthe semiconductor device 20 a.

Further, as illustrated in FIG. 18, the inspecting device 10 may beconfigured as a separate body from the laser processing device 1. Theinspecting device 10 illustrated in FIG. 18 includes a stage 101, adrive unit 102, and a control unit 103 in addition to the imagecapturing unit 4. The stage 101 is configured similar to the stage 2described above, and supports a wafer 20 in which a plurality of rows ofmodified regions 12 are formed. The drive unit 102 supports the imagecapturing unit 4 and moves the image capturing unit 4 along theZ-direction. The control unit 103 is configured similar to the controlunit 8 described above, and functions as the inspection part. In a laserprocessing system illustrated in FIG. 18, the wafer 20 is transportedbetween the laser processing device 1 and the inspecting device 10 by atransporting device such as a robot hand.

In addition, the irradiation condition of the laser light L when thewafer 20 is irradiated with the laser light L from the back surface 21 bside of the semiconductor substrate 21 along each of the plurality oflines 15 are not limited to those described above. For example, asdescribed above, the irradiation conditions of the laser light L mayinclude a condition that the fracture 14 extending through a pluralityof rows of the modified regions 12 (for example, two rows of modifiedregions 12 a and 12 b) reaches an interface between the semiconductorsubstrate 21 and the functional element layer 22. Alternatively, theirradiation condition of the laser light L may be a condition that thefracture 14 extending through a plurality of rows of the modifiedregions 12 reaches the front surface of the functional element layer 22on an opposite side of the semiconductor substrate 21. Alternatively,the irradiation condition of the laser light L may be a condition thatthe fracture 14 extending through a plurality of rows of the modifiedregions 12 reaches the vicinity of the front surface 21 a in thesemiconductor substrate 21. As described above, the irradiationcondition of the laser light L may be any condition as long as thefracture 14 extending through a plurality of rows of modified regions 12is formed. In any case, it is possible to check whether or not thefracture 14 extending through a plurality of rows of modified regions 12is sufficiently extend to the front surface 21 a side of thesemiconductor substrate 21.

Various materials and shapes can be applied to each configuration in theabove-described embodiment without being limited to the above-describedmaterials and shapes. Further, the configurations in the embodiment orthe modification examples described above can be randomly applied to theconfiguration in another embodiment or modification examples.

REFERENCE SIGNS LIST

-   -   2 stage    -   8 control unit (inspection part)    -   10 inspecting device    -   12, 12 a, 12 b modified region    -   14, 14 a fracture    -   14 e tip    -   15 line    -   20 wafer    -   20 a semiconductor device    -   21 semiconductor substrate    -   21 a front surface    -   21 b back surface    -   22 functional element layer    -   22 a functional element    -   41 light source    -   43 objective lens    -   43 a correction ring    -   44 light detection part    -   F focus    -   Fv virtual focus    -   I1 light    -   L laser light    -   R1 inspection region

The invention claimed is:
 1. A laser processing method comprising: afirst step of preparing a wafer including a semiconductor substratehaving a front surface and a back surface and a functional element layerformed on the front surface, and forming a plurality of rows of modifiedregions in the semiconductor substrate along each of a plurality oflines by irradiating the wafer with laser light from the back surfaceside along each of the plurality of lines; and a second step ofinspecting whether or not there is a tip of a fracture in an inspectionregion between the front surface and the modified region closest to thefront surface among the plurality of rows of modified regions, thefracture extending to the front surface side from the modified regionclosest to the front surface, wherein in the first step, the wafer isirradiated with the laser light from the back surface side along each ofthe plurality of lines under a condition that a fracture extendingthrough the plurality of rows of modified regions is formed, and in thesecond step, whether or not there is the tip in the inspection region isinspected by aligning a focus from the back surface side to a region onan opposite side of the back surface with respect to the front surface,positioning a virtual focus symmetrical with the focus with respect tothe front surface in the inspection region, and detecting lightpropagating in the semiconductor substrate from the back surface side tothe back surface side via the front surface.
 2. The laser processingmethod according to claim 1, wherein in the first step, the wafer isirradiated with the laser light from the back surface side along each ofthe plurality of lines under a condition that the fracture extendingthrough the plurality of rows of modified regions reaches the frontsurface.
 3. The laser processing method according to claim 2, furthercomprising: a third step of evaluating a processing result in the firststep, based on an inspection result in the second step, wherein in thethird step, it is evaluated that the fracture extending through theplurality of rows of modified regions reaches the front surface, in acase where there is no tip in the inspection region, and it is evaluatedthat the fracture extending through the plurality of rows of modifiedregions does not reach the front surface, in a case where there is thetip in the inspection region.
 4. The laser processing method accordingto claim 1, wherein the plurality of rows of modified regions are tworows of modified regions.
 5. A method for manufacturing a semiconductordevice, the method comprising: the first step, the second step, and thethird step of the laser processing method according to claim 3; and afourth step of, in a case where it is evaluated that the fractureextending through the plurality of rows of modified regions reaches thefront surface in the third step, exposing the fracture extending throughthe plurality of rows of modified regions to the back surface bygrinding the back surface, and cutting the wafer into a plurality ofsemiconductor devices along each of the plurality of lines.
 6. Aninspecting device comprising: a stage configured to support a waferincluding a semiconductor substrate having a front surface and a backsurface and a functional element layer formed on the front surface, thewafer in which a plurality of rows of modified regions are formed in thesemiconductor substrate along each of a plurality of lines; a lightsource configured to output light having transparency to thesemiconductor substrate; an objective lens configured to pass the lightoutput from the light source and propagated through the semiconductorsubstrate; a light detection part configured to detect the light passingthrough the objective lens; and an inspection part configured to inspectwhether or not there is a tip of a fracture in an inspection regionbetween the front surface and the modified region closest to the frontsurface among the plurality of rows of modified regions, based on asignal output from the light detection part, the fracture extending fromthe modified region closest to the front surface to the front surfaceside, wherein the objective lens aligns a focus from the back surfaceside to a region on an opposite side of the back surface with respect tothe front surface and positions a virtual focus symmetrical with thefocus with respect to the front surface in the inspection region, andthe light detection part detects the light propagating in thesemiconductor substrate from the back surface side to the back surfaceside via the front surface.
 7. The inspecting device according to claim6, wherein the objective lens has a numerical aperture of 0.45 or more.8. The inspecting device according to claim 6, wherein the objectivelens includes a correction ring.